WOOD RESEARCH Volume 67, Number 6, 2022
Boháček Štefan, Pažitný Andrej, and Michaela Handlovská

Intensification of the freeze-thaw pretreatment of disintegrated poplar wood

This research was focused on the effect of water content in the cells of disintegrated Populus nigra L. on a freeze-thaw pretreatment method before an enzymatic hydrolysis. Two chipped and sieved fractions 2.5 mm and 0.7 mm and two milled fractions, characterized as 18°SR (Shopper–Riegler index) and 37°SR, of the disintegrated 5 years old poplar tree were used for our experiment. Glucose and xylose yields were measured after 24 and 48 hours of enzymatic hydrolysis with a 15% load of the enzyme measured to a total cellulose content. The influence of nine freeze-thaw cycles under -20°C and +20°C was considered. The results showed that an increase in moisture content positively affects yields in all fractions but a desirable result was achieved mainly for the 0.7 mm fraction where the total yield increased by about 16%. More effective way is a finer wet beating of wood mass, while wood fibre receives moisture already in the technological process. The highest glucan conversion 51,74% and the total hemicelluloses conversion 47,72% was achieved for the finest fraction 37°SR. The higher moisture content has a positive effect on the increase in the conversion of oligosaccharides, especially glucan, in chipped fractions.

WOOD RESEARCH Volume 61, Number 5, 2016
Zuzana Brezániová, Mária Fišerová, Monika Stankovská, Juraj Gigac, Elena Opálená, and Jarmila Puškelová

Effect of prehydrolysis on enzymatic hydrolysis of two-stage pretreated wheat straw

The effect of water prehydrolysis conditions, which was used as the first stage of wheat straw pretreatment, on the composition of filtrates was analysed. Many of the substances that are present in the prehydrolysis filtrates are broadly used and thus they contribute to improvements in the efficiency of bioethanol production. Prehydrolysis was carried out at temperatures of 140, 160 and 180°C and times of 30, 60 and 120 min. Xylose and its oligomers were the most represented in prehydrolysis filtrates, their yields increased up to 12.1 % with increasing weight of wheat straw removed up to 28.6 %. Besides xylose and glucose, acetic acid, formic acid and the phenolic compounds were also present in the prehydrolysis filtrates. At 160 and 180°C, levulinic acid and furfural and hydroxymethylfurfural, respectively, were also present. The solid fractions of wheat straw were subjected to steam explosion under the same conditions at 200°C for 2 min. Two-stage pretreated wheat straw was subsequently enzymatically hydrolysed. The conditions of water prehydrolysis combined with steam explosion pretreatment had a significant effect on the results of enzymatic hydrolysis of wheat straw. The conversion of cellulose increased with increasing prehydrolysis temperature and time from 64.8 to 91.7 %. Similar results were observed for the conversion of xylan from 73.7 to 92.4 %. With increasing of prehydrolysis temperature and time, the amount of inhibitors in hydrolysates decreased. The recommended conditions for water prehydrolysis at two-stage pretreatment of wheat straw correspond to temperature of 160°C and time of 60 min.

WOOD RESEARCH Volume 61, Number 1, 2016
Albert Russ, Mária Fišerová, Michal Letko, and Elena Opálená

Effect of steam explosion temperature on wheat straw enzymatic hydrolysis

Wheat straw is an abundant and readily available lignocellulosic material potentially suitable for the second generation bioethanol production. Steam explosion was investigated as a suitable pretreatment method. Effect of steam explosion temperature on wheat straw enzymatic hydrolysis was investigated. Optimum steam explosion temperature at around 200°C was determined based on concentration of monosaccharides in hydrolysates, conversion of cellulose and xylan and yield of monosaccharides from wheat straw. This corresponds to creating conditions resulting in sufficient damage to the lignocellulose structure which leads to higher enzyme accessibility. Lower temperature does not enable sufficient enzyme accessibility while excessively high temperature results in significant breakdown of monosaccharides and lignin and creation of inhibitors. The amount of originated inhibitors was also determined for each studied steam explosion temperature.

WOOD RESEARCH Volume 62, Number 6, 2017
Juraj Gigac, Mária Fišerová, Monika Stankovská, and Pažitný Andrej

Enzymatic hydrolysis of extruded wheat straw with addition of sodium hydroxide and calcium hydroxide

Extrusion pretreatment of wheat straw in a single screw extruder was investigated in terms of effectiveness of enzymatic hydrolysis and the formation of fermentation inhibitors. The effect of sodium hydroxide in extrusion pretreatment was compared with calcium hydroxide. The accessibility of wheat straw structure to hydrolytic enzymes increased with NaOH and Ca(OH)2 loadings, whereby more with the addition of NaOH. With 6% w/w of NaOH loading, the conversion of polysaccharides was 76.1% and with the same Ca(OH)2 loading it was 47.3%. The conversion of polysaccharides with 12% w/w of Ca(OH)2 loading was 66.6%. Without alkali in extrusion pretreatment, the conversion of polysaccharides was only 36.7%. The polysaccharides conversion of original extruded wheat straw was about 1.5 to 3.3% higher in comparison to washed extruded wheat straw. Fermentation inhibitors such as lignin, acetic and formic acid are primarily formed in the presence of alkali during extrusion pretreatment, most of which was lignin. Alkaline extrusion is a suitable method for pretreatment of lignocellulosic biomass.